Thursday's sixth Republican presidential primary debate — the second to air on Fox Business Network — was watched by 11 million viewers and 3 million in the advertiser-friendly adults 25-54 demographic, according to preliminary numbers from Nielsen. That's down a bit from the 13.5 million that tuned in to the net's first debate last November, but it was enough to give FBN the No. 1 program on all of cable news.

Moderated by Neil Cavuto and Maria Bartiromo, it was also the second-highest-rated program in network history and drove 1.165 million peak concurrent streams, just behind FBN’s 1.4 million streams in November.

The falloff is not unexpected. It was the sixth Republican debate in a record-breaking presidential primary cycle where the first debate last August on Fox News Channel became the most watched nonsports program in basic cable history with 24 million viewers. Since then, the debates among Republicans and Democrats have slowly shed viewers.

Last night's debate still had plenty of fireworks. With Texas Sen. Ted Cruz leading the polls in Iowa — home of the first caucuses in February — Cruz and national frontrunner Donald Trump engaged in repeated heated exchanges, including over Trump's questioning of Cruz's birth in Canada and Cruz's pejoratively referring to Trump as having "New York values."

The latter spat produced one of the debate's most memorable moments when co-moderator Maria Bartiromo, who pointed out that she is from New York, pointedly asked Cruz to explain what he meant.

"Everyone understands that the values of New York City are socially liberal, are pro-abortion, are pro-gay marriage," Cruz said.

Trump effectively neutralized the criticism by emotionally evoking the Sept. 11, 2001, terrorist attacks during which 2,996 New Yorkers were killed.

"When the World Trade Center came down, I saw something that no place on Earth could have handled more beautifully, more humanely than New York. You had two 110-story buildings come crashing down. I saw them come down. Thousands of people killed, and the cleanup started the next day, and it was the most horrific cleanup, probably in the history of doing this. I was down there, and I've never seen anything like it. And the people in New York fought and fought and fought. And we saw more death, and even the smell of death — nobody understood it. And it was with us for months, the smell, the air," said Trump.

"And we rebuilt downtown Manhattan, and everybody in the world watched and everybody in the world loved New York and loved New Yorkers. And I have to tell you, that was a very insulting statement that Ted made."